Despite the latest technological advancements made in railway track design, material development, and construction methodology, rail movement due to temperature variations still remains a costly and formidable challenge to many in the maintenance of way profession. Longitudinal expansion in rail due to radiant heating by the sun in summer causes track distortion and buckling, but successive contraction in winter also causes breakage in rail. This natural opposing behavior of rail has revealed its prominence and impact on operational safety and cost since the birth of railroad. Especially in territories where drastic difference in temperature encountered in seasonal change, difficulty level for the task in maintaining a safe railroad often magnifies itself exponentially under extreme weather conditions. Heat elicits shape change in material whose behavior is governed by physical properties, but no matter how distinctive physical change may vary in magnitude, all materials respond simultaneously in similar manner when subjected to heat or cold. The technique currently employed to cope with rail expansion problem on the railroad is by rail anchoring and rail length adjusting with cutting and welding to maintain track stability. Over the years, the railroad industry as a whole seems saturated in belief that rail thermal expansion in track is an inherent physical fact of life, and satisfied by the effective counter measure in place. The industry also has learned to live with a track structure with perpetual movement and instability, and contemplated that the threat of heat is only temporary during the day. Once temperature goes down, the problem resolves by the natural process of heat dissipation in the air. This is probably the reason leading to numerous inventions related to the prior art in the development of more restraining products and railroad tie systems, and yet not much is evident in gain of new technology departing from it with resolution to reducing the amount of heat exchanged in the rail.
The common term “Heat” is defined as internal energy or more precisely as thermal energy that flows from a system of relatively high temperature to one at a relatively low temperature. It is also called molecular translational energy due to the kinetic nature of molecule movement. Temperature is defined as a measure of the average molecular translational energy in a system, and the greater the change in temperature for most materials, the greater the amount of thermal expansion or contraction.
Using the value of 0.12 BTU/lb.° F. as specific heat Cp for rail steel, the weight of 45.3333 lb./ft. for a 1,500 ft. long 1361b. RE rail, and a temperature change of 60° F., the change of internal energy will be:Q=45.3333 lb./ft.×1500 ft.×0.12 BTU/lb.° F.×60° F.Q=489,600 BTU or 143.28 KWH
When a rail is free to move without restraint, it changes 0.0000065 inch per inch of its length per degree Fahrenheit change in temperature. Therefore the same rail of 1,500 feet long undergoes a temperature change of 60° F., a normal linear expansion of 7.02 inches will result as the addition in length. In railroad operation, this physical expansion must be restrained for practical reasons. It is accomplished by application of rail anchors or elastic fasteners appropriately in consideration of track geometry and rail laying arrangement. However the method employed to stop rail movement also gives rise to an internal force equal and opposite the sum of restraining forces applied by the restraining appurtenances.
For every 1° F. change in temperature, 195 psi is the internal stress set up in the rail by restraining forces, based on the stress-strain relationship of:Stress=0.0000065 in/in×30,000,000 psi×ΔT° F.Consequently, to restrain a 1361b RE section rail with a cross-sectional area of 0.0929 sq.ft. (13.3776 sq.in.) and with a temperature change of 60° F.:Force=Area×195 psi/° F.×ΔT° F.Force=13.3776 sq.in.×195 psi/° F.×60° F.=156,518 lbs. or 78.26 tonsWhen the rail is restrained in such a way that its expansion disallowed but yet its internal energy increases due to rise in temperature, the force developed internally is compressive in nature. Therefore, the rail is said to be in compression. Catastrophic failure in lateral distortion (bulge) out of straightness is called track buckling.
Contrary to foregoing, when the rail is restrained and disallowed to contract, the force developed internally is tensile in nature. Subsequently, the rail is in tension. Catastrophic failure in rail breakage is called pull apart.
Conspicuously, the impact on railroad track structure by forces in such magnitude cannot be ignored while railroads operate to comply with stringent safety requirements and the insatiable demands for higher speed and axle load from freight and passenger traffic. Buckled track has always been a major concern in the railroad industry. Incidents of such occurrence often lead to derailment and wreckage, and have been steadily growing since the introduction of the Continuous Welded Rail (CWR). Industry-wide in the United States, railroads are experiencing numerous buckled track derailments each year. By nature of safety concern for rail passengers, communities adjacent to railroad right of way, and hazardous material freight operations, no railroad or transit authority can tolerate risk of buckled track. In a different perspective, some argue that buckled track is not a cause but the consequence of some deficiency in the track structure or track maintenance procedures. A properly constructed and maintained piece of track should not buckle from thermal loading during normal seasonal variations of temperature. Something else, whether or not apparent to the naked eyes, must be present for buckling to occur, such as misalignment, inadequate ballast section, loss of neutral temperature, rail anchor deficiency, elastic fastener deficiency, and inadequate water drainage etc.
In another aspect, thermal forces developed in the rail remain in the track system, and the magnitude of these forces is proportional to the rail temperature. Therefore, the risk for a track to buckle is higher when the temperature is higher. The culpable factor is the heat, and because of it problem follows. Although good construction and maintenance practice to resolve this problem by applying powerful and sophisticated restraining device to control rail movement and transfer the load to the ground, the method does not remove heat from the rail. Rail anchors and elastic fasteners transmit thermal forces to the railroad ties. The railroad ties are in turn restrained by the track ballast. Therefore any change to the soil condition that compromises the delicate balance may release these forces, and often suddenly lead to catastrophic consequences. Since the occurrence of track buckling is directly related to radiant heating by the sun, it is often called Sun Kink.
To combat track buckling or sun kink, CWR track must be carefully laid and adjusted to the neutral temperature of the area. The method of heating to expand rail is often used to lay or adjust CWR track, if the actual rail temperature is less than the neutral temperature. The amount of rail adjustment must be calculated based on the difference of the rail actual temperature and the desirable neutral temperature, the length of rail to be adjusted, and the coefficient of expansion for rail steel. Space equal to the amount of expansion needed for each string of CWR should be provided between the end of that string and the near end of the next adjacent string. A minimum of 10 ties should be box anchored on the near end of the adjacent string to hold it in place and avoid closing the expansion gap of the string being heated. The rail also needs to be tapped slightly with sledgehammer to free itself from friction sitting on tie plates and advance in the direction of expansion. Uniformity of expansion is controlled by marking each quarter of the string and introducing expansion as ¼ point, ½ point, and ¾ point. CWR should be heated so that expansion is introduced from one end of each string to the other. Heat should be steadily applied while moving forward until the required expansion has been obtained at the end of each string. As adjusting in progress, a minimum of 4 ties should be boxed anchored per 39′ of rail to prevent the rail from losing adjustment. At the end of the completely expanded string, a minimum of 20 ties should be box anchored immediately after the gap is closed to hold the expansion.
Standard practice of track maintenance requires an adequate ballast section. To reduce lateral and vertical sun kinking, full cribs, good drainage, and sufficient shoulders of satisfactory grade ballast are required. A minimum shoulder of 6 inches is mandatory, but for safe dependable restraint under all thermal and axle load conditions, a 12 inches shoulder is preferred. Continuous welded rail track should be disturbed as little as possible, and should not be disturbed at all for maintenance purposes when in compression and showing signs of possible displacement, for example observation of edge space in tie crib and series of directional movement of rail anchors along rail base. Any disturbance to ballast compaction lessens lateral restraint against sun kinks, and a high percentage of such occurrences resulted in derailments. When a sun kink occurs under a train, the derailment usually occurs with several cars behind the locomotive. Because the rail tends to expand in the direction of least resistance, it often expands upward sufficiently to free it from lateral restraint and then it distends laterally. Sun kinks are likely to occur in the spring as the rail adjusts to the warmer weather, and again in the fall as colder temperatures call for a change in summer procedures.
Anchoring continuous welded rail (CWR) track usually calls for box anchoring every tie for 200 feet on each end of the CWR string, and also at railroad crossing approaches, and then box anchor every other tie in between to protect against rail breaks and normal running. Conventional CWR tie restraint is practiced on ballast deck bridges but not on open-deck structures, where damage to bridge timber would occur. With short single spans it is customary to box-anchor every tie for 200 feet at each end of the bridge and omit rail anchors on the bridge deck. For longer structures either jointed rail is used or one or more sets of expansion joints are installed to allow for unrestrained rail movements. Due to the unrestrained rail movement on open-deck bridge or similar structures, operational issue persists in hot summer months regardless of high maintenance efforts and costs to ensure safe operation of train traffic over these structures.
Historical development of the heat pump dates back in time of Lord Kelvin, William Thomson, in Great Britain 1852, and in association with his famous work “The Theory of Dissipation of Energy”. In several papers on this subject, he pointed out that motive power was obtained only by ‘degrading’ heat, i.e. burning fuel, and that the heat thereby rejected represents energy dispersed and ‘unavailable’ as further motive power. He therefore outlined and designed a machine which he called a Heat Multiplier, the predecessor of what we are familiar with today as Heat Pump. This machine would permit a room to be heated to a higher temperature than the ambient temperature, by using less fuel in the machine than if such fuel was burned directly in the furnace. However, a real machine for heating building using Kelvin's cycle and specification was never built in U.K. at the time of disclosure despite of her critical fuel resources. Unlike in the United States where the number of domestic heat pumps used for either space cooling or heating exceed millions. Heinrich Zoelley patented the idea of using heat pump to draw heat from the ground in 1912. The first commercial heat pump was put in use to heat the Commonwealth Building in Portland Oreg. in 1946.
Today, geothermal ground source heat pump is commonly used in the HVAC system for the LEED accredited building projects, not just for promulgating an image of green or sustainable energy utilization but for operating cost saving on a long range basis. It is a central heating or cooling system that pumps heat to or from the ground. It uses the earth as a heat source in the winter or a heat sink in the summer. The upper 10 feet of Earth's surface maintains a nearly constant temperature between 50° F. and 60° F. Like a refrigerator or air conditioner, the system uses a heat pump to force the transfer of heat to and from the ground. Heat pump transfers heat from a cool space to a warm space, against the natural direction of flow, or it can enhance the natural flow of heat from a warm area to a cool one. The core of the heat pump is a loop of refrigerant pumped through a vapor-compressor refrigeration cycle that moves heat. A refrigeration cycle is comprised of operations by a compressor, condenser, expansion valve, and evaporator. The refrigerant agent vapor enters the compressor through the suction port from the evaporator, compressed and then ejected with high temperature and high pressure to the condenser coil. In the condenser coil, the superheated refrigerant vapor must give up its heat and turns into liquid and accumulates in the liquid receiver before reaching the restrictive expansion valve. Once passing through the expansion valve, this refrigerant liquid is allowed to expand and boil vigorously become vapor again in the evaporator coil. Since the phase change from liquid to vapor necessitates latent heat of evaporation, heat must be drawn from the surrounding of the evaporator coil to sustain this physical transformation. Therefore heat is taken in by the refrigerant vapor while moving through the evaporator coil before reaching the suction portion of the compressor for the repeated process. The evaporator and condenser exchange heat with the space surrounding, and with the water-glycol solution which absorbs or dissipates heat through the tubing loop system buried underground. Since heat is taken away from the space surrounding, it provides cooling effect to the space. Reversibly, by exchanging the flow, the system provides heating effect to the space. This process continues until the desirable temperature for the room space has been reached.